User applications for personal computers and other computer devices increasingly rely on a link to a communications network such as the Internet. Stationary PC systems may be linked to a network using various techniques: via traditional or high-speed digital phone lines, via office computer networks and via cable TV networks, among others.
The increasing reliance on a data network link for PC applications has fueled a demand for wireless communication technology to serve portable computing devices such as PC notebooks. One technical approach involves operably linking a modem-equipped PC notebook to a portable radio telephone of a wireless phone network. Users have identified the linking of two separate devices, i.e. the phone and the computer, as cumbersome, however.
The market for portable computing devices favors lighter and smaller designs while demanding the same functions as stationary systems. Options for modular expansion are therefore limited. Many PC notebooks and other computers, as well as some computing devices are designed to receive plug-in, removable expansion cards. Notebook computer manufacturers have almost universally adopted a standard expansion card interface established by the Personal Computer Memory Card International Association (PCMCIA), Sunnyvale, Calif. These standards define the electrical and physical specifications of the card including the interfaces between the card and the port or slot into which the card is inserted.
The specifications include a 16-bit PC Card interface and a 32-bit CardBus interface. The PCMCIA standards also specify three card form factors, called Type I, Type II and Type III. All three card types measure the same length (85.6 mm) and the same width (54.0 mm), and differ only in overall thickness. The Type I card has a thickness of 3.3 mm; the Type II card, 5.0 mm; and the Type III card, 10.5 mm. The PCMCIA interface is described in detail in the PCMCIA Specification (i.e., Personal Computer Memory Card International Association—PCMCIA Standard Release 2.1) which is hereby incorporated by reference.
There continues to be a need for a single PC card that provides both the transceiver function of a portable phone and the modem function. The PCMCIA standard imposes strict size constraints on the design of such a multifunction expansion card, however. The thickness specification—0.5 mm—of the popular Type II card particularly limits the thickness profile of all required electronic components.
This profile constraint has limited the selection of a key RF transceiver component, the antenna duplexer. Compared to other duplexer alternatives, ceramic block-based antenna duplexers are known to offer better performance at relatively low cost.
Such ceramic block filters offer several advantages. In the basic ceramic block filter design, the resonators are formed by passages, called holes, extending through the block from the long narrow side to the opposite long narrow side. The block is substantially plated with a conductive material (i.e. metallized) on all but one of its six (outer) sides and on the inside walls formed by the resonator holes.
One of the two opposing sides containing holes is not fully metallized, but instead bears a metallization pattern designed to couple input and output signals through the series of resonators. This patterned side is conventionally labeled the top of the block. In some designs, the pattern may extend to sides of the block, where input/output electrodes are formed and the block is surface mounted to a PCB.
The reactive coupling between adjacent resonators is dictated, at least to some extent, by the physical dimensions of each resonator, by the orientation of each resonator with respect to the other resonators, and by aspects of the top surface metallization pattern. Interactions are complex and difficult to predict. These filters may also be equipped with an external metallic shield attached to and positioned across the open-circuited end of the block in order to cancel parasitic coupling between non-adjacent resonators and to achieve acceptable stopbands.
The relatively large size of the ceramic block duplexer has limited their application for PCMCIA cards. The invention relates to this size limitation problem.